1. Technical Field of the Invention
The present invention relates to an automatic focusing projector for giving an object a distance measuring contrast whenever the object has low illuminance or a small natural contrast. The present invention further relates to the use of a color filter in such a projector which is adapted to be used in combination with a white light source.
2. Description of Related Art .
Generally, automatic focusing projectors of the type disclosed by the present application are usually incorporated in automatic focusing cameras in which information representative of the distance of an object from the camera can be given by contrast in the object. Namely, when an object has a low illuminance or a small contrast, e.g., a white wall, insufficient contrast is obtained from such an object, and, accordingly, a contrast pattern must be projected onto the object to enable automatic focusing. Such a system is disclosed in commonly assigned U.S. patent application Ser. No. 029,924, of which the present application is a continuation-in-part.
FIG. 5, which is labelled prior art, illustrates the principle of such an automatic focusing projector, which is per se known. In such a projector, rays of light emitted from a light source 11 are transmitted, via a chart 12 which has a predetermined contrast pattern, e.g., alternating light and dark fringes, and are then projected onto an object 14 through a projecting lens 13 to provide a contrast on the object being photographed.
FIG. 4, also labelled as prior art, illustrates a known projector which is used in the optical system illustrated in FIG. 5. This known projector includes an elliptical mirror 15 which has a lamp (i.e., a light source) 16 located at a first focal point Fl of the elliptical mirror 15 and an exit opening 17 through which rays of light can be emitted. Opening 17 is located at an end of the elliptical mirror 15 which is close to a second focal point F2 thereof. Contrast chart 12 is positioned in front of opening 17, outside (and forwardly) of elliptical mirror 15. A projecting lens 13 is positioned forWardly of contrast chart 12 (having a patterned surface).
In this type of known projector, light from light source (i.e., lamp) 16 passes through second focal point F2, either directly or after reflection by the inner surface of mirror 15, and the light is then projected outwardly from elliptical mirror 15 through opening 17, so that the contrast pattern of contrast chart 12 is projected onto the object through projecting lens 13.
However, in the known projector illustrated in FIG. 4, almost all of the inner surface of the elliptical mirror must be used in order to project the contrast pattern on the object, necessarily resulting in an increased size for the whole optical system. In addition to this, since rays of light in the cross-hatched areas S shown in FIG. 4 cannot be utilized, the efficiency of light use is decreased. It is thus necessary to increase the size of projecting lens 13 in order to use all of the rays of light.